A TBCC engine would use a conventional turbojet to achieve speeds up to about Mach 3, the limit for a turbojet, and then transition to a dual ramjet/scramjet, which must be traveling at speeds over Mach 3 to work properly, compressing air from the intake to achieve combustion without an axial compressor. The ramjet/scramjet would then carry an aircraft to speeds over Mach 5. The plane would need to transition back to to the turbojet to slow down and land.